Screw propeller



April 20, 1965 s. FUCHS SCREW PROPELLER 2 Sheets-Sheet 1 Filed June 14, 1962 INVENTOR Gyula Fuchs flxial Distance ATTORNEYS April 20, 1965 e. FUCHS SCREW PROPELLER 2 Sheets-Sheet 21 Filed June 14, 1962 INVENTOR Gyula Fuchs W *1 MM ATTORNEYS United States 3,179,182 SCREW PROPELLER Gynla Fuchs, Lakewood, Ohio, assignor of thirty-three percent to llmre Papai and seven percent to Sigmund T. Brinsky, in trust, both of Cleveland, Ohio Filed June 14, 1962, Ser. No. 202,482

16 Claims. (Cl. 170-156) The present invention relates to a marine propeller and in particular to a double blade screw propeller wherein each blade extends slightly more than half-way around the circumference.

For the last 50 years, propellers for ships have been provided with 3 or 4 blades each extending only a short distance around the circumference, it being thought that propellers of this type had the highest efliciency and would provide the ship with the maximum speed. Prior to this invention, it was thought that water screws were inefficient and were not suitable means for propelling boats or ships. 7

For many years attempts have been made to increase the speed of ships and to provide improved propellers for such ships. Although great advances were made in the power plants for the ships, the speed of the ships was limited because of the limitation of the known types of propellers. Thus, in recent years ship builders have been frustrated by having available nuclear power plants which cannot utilize their full power because of the inadequacy of the ship propellers.

It has now been discovered that ships can be propelled at high speeds using a screw-type propeller having two relatively thin spiral blades each extending circumferentially more than 180 and being shaped to provide high efficiency. Each blade, although thin, has adequate strength to transmit large amounts of power. The screw propeller functions efiiciently even when it has a relatively large angular pitch in excess of 22 (i.e., 24 to 27). It is thus possible to propel a boat at high speed even though the rotational speed is relatively low compared to that of conventional propellers.

An object of the invention is to provide a marine screw which is capable of transmitting large amounts of power and is capable of propelling a boat or ship at a high speed.

Another object of the invention is to provide ship propulsion means which is eflicient when propelling the ship at high speeds.

A still further object of the invention is to provide a propelling means for ships which has adequate strength to transmitlarge amounts of power.

3,179,182 Patented Apr. 20, 1965 FIGURE 7 is a fragmentary sectional view taken on the line '7-7 of FIGURE 2;

FIGURE 8 is a fragmentary sectional view taken on the line $-8 of FIGURE 2; and

FIGURE 9 is a fragmentary sectional view taken on the line 9-9 of FIGURE 2 and on the same scale as FIG- URES 6 to 8, the medial radius being shown in dot-dash lines.

Referring more particularly to the drawings in which like parts are identified by the same letters and numerals throughout the several views, FIGURES 1, 2 and 3 show a double-blade marine screw or propeller S rigidly mounted on a horizontal drive shaft 1 having a collar 2 and an axially elongated tapered portion 3 of reduced diameter which is externally threaded at the end to receive a nut 4 having a projecting nose 5. In order to permit keying of the screw propeller to the drive shaft, said reduced portion 3 is provided with a narrow keyway 6.

The screw of the present invention is preferably formed as a one-piece metal casting or forging comprising an axially elongated hubd and two integral pitched coaxial blades 9 and 10 of the same size and shape projecting radially from said hub and having corresponding portions of the two blades spaced 180 apart. The hub 8 has a tapered bore 11 coaxial with the blades and of the same size as the reduced portion 3. The leading end of the hub has a flat surface 12 perpendicular to the axis for engaging the corresponding fiat surface of the collar 2, and the trailing end of the hub has a similar flat surface 13 perpendicular to said axis for engaging the washer 14.

The channel 15 formed between the blades 9 and 10 is generally helical and preferably has a width not materially less than its radial depth as. shown, for example, in FIG- URE 4. The channel 15 preferably has a rounded bottom surface 16 extending between the blades and side surfaces 17 and 18 which are generally perpendicular to the axis of rotation. The surface 17 comprises the leading face of each spiral blade and the surface 18 comprises the trailing face of that blade. The surfaces 17 and 18 are smooth and free of reversals in radial curvature outwardly of the medial radius M The medial radius is half the radius of the blade and is indicated in dot-dash lines in FIGURES 6 to 9.

Each of the blades 9 and 10 has a leading end portion 20 and a trailing end portion 21 in the form of a rounded lobe, the trailing portion of one blade overlapping the leading portion of the other blade by more than 10 degrees and preferably by 20 or 30 degrees. The leading end Another object of the invention is to provide a ship prop peller having a very high pitch and capable of delivering large amounts of power at relatively low rotational speeds.

Other objects, uses and advantages of the invention will become apparent from the following description and claims and from the drawings in which:

FIGURE 1 is a side elevational view on a reduced scale showing the double-blade screw propeller of this invention;

FIGURE 2 is an end view of the screw of FIGURE 1;

FIGURE 3 is a sectional view taken substantially on the line 33 of FIGURE 1 and on the same scale looking at the opposite end of the screw;

. FIGURE 4 is a fragmentary sectional view through the axis of the screw taken substantially on the line 44l of FIGURE 2 and on the same scale;

FIGURE 5 is a diagrammatic view showing the spiral edge of one blade laid out in a flat plane;

. FIGURE 6 is a fragmentary sectional view taken on the line 6--6 of FIGURE 2 and on a larger scale;

portion 20 has a straight cutting edge 22 substantially perpendicular to the axis of rotation and extending more than half the distance from the hub 8 to the periphery of the blade. The leading portion 20 has a curved edge portion 23 which extends radially a small fraction (i.e., A to A1) of the blade radius and has a curved edge portion 24 adjacent the hub which is curved in the opposite direction as indicated in FIGURE 3. A major portion of the leading edge of the blade portion 20 outwardly of the medial radius is generally perpendicular to the axis of rotation so that the blade cuts into the water in the most efficient manner. The curved edge 23 is tangent to the cutting edge 22 at the point aa and is tangent to the edge 25 in the vicinity of the point a. r

The lobe 21 has a smoothly curved trailing edge 26 rangent to the outermost edge 25 of the blade and extending substantially from said outermost edge to the hub 8. The radius of curvature at any point on the edge 26 is preferably in the range of 0.4 to 0.5 times the radius of the blade as shown, for example, in FIGURE 2 which is drawn substantially to scale. Best results are obtained when at least the radially outer half of the edge 26 has a radius of curvature within said range. All of the are 26 outwardly of the point 27 should have a curvature within that range, the point 27 being located at the medial radius M Adjacent the hub S the lobe 21 has a reversely curved edge portion 28. The lobe 21 preferably has a cup-shaped portion 29 on the leading face 17 adjacent the hub 8 to improve the efficiency of the screw.

The outermost edge 25 is in the form of a spiral having a generally uniform pitch. Such edge extends circumferentially about one-half revolution as indicated in FIG- URES 2 and 3. Points a through along the marginal edge of the blade 9 are shown in FIGURE 2. Corresponding points on the blade 10 are identified by the letters a through x. The sections 65 and 99 do not pass through any of the latter points; and, therefore, the outermost point in FIGURE 6 is identified as mm and the outermost point in FIGURE 9 is identified as 2].

FIGURE is a diagrammatic view on a reduced scale showing the appearance of the edge 25 when it is laid out in a flat plane, the ordinate representing the circumferential distance and the abscissa represents the axial distance from points on the line 25 to the plane 33 containing the end surface 12 of the hub. It is apparent from FIGURE 5 that the pitch is generally uniform (as indicated by the angle A) but that there is a slight curve near the ends of the line 25.

While the exact shape of the marine screw of this invention may vary considerably, the location of the points on the edge of the blades is indicated in Table I for purposes of illustration. In this table 0 is the angle in degrees, D is the axial distance in inches from the plane 3-3 containing the end surface 12 of the hub, and D is the radial distance in inches from the point to the axis of rotation. This table applies to the screw shown in the drawings which has a radius R of 5.5 inches. It will be understood that the numbers set forth in Table I are approximate and that these may be varied considerably without departing from the invention.

Table l 0 0 D Dr a a 190 0. 68 5. 5 1) l) 200 1.17 5. 5 a 0 210 1. 63 5. 5 d (1 220 2. 00 5. 5 a (2 230 2. 37 5. 5 f 00 f' 240 2. 74 5. 5 9 {1' 250 8. 06 5. 5 h h 260 3. 35 5. 5 1 i 270 3. 64 5. 5 j j 280 3. 02 5. 5 It k 290 4. 17 5. 5 l 1 300 4. 41 5. 5 m m 310 4. 02 5. 5 n n 320 4. 83 5. 5 0 0 330 5. 04 5. 5 1) p 340 5. 24 5. 5 1 g 350 5. 41 5. 5 T 180 T 360 5. 58 5. 4 8 3 10 5. 75 5. l t 200 t 20 5. 92 4. 6 u 210 11. 0 a 220 0 3 w 230 w 50 6. 4 2. 3 z 235 x 55 6. 4 1. 7

The thickness of each of the blades 9 and 10 gradually decreases in a radial direction from the hub 8 to the peripheral edge 25 and gradually increases in a circumferential direction from the leading end portion 20 to the trailing end portion 21. Such variation in thickness is indicated in Table II below. The average rate of change in thickness is preferably 0.2 to 0.3 percent per degree of circumference, but this is not essential. The maximum rate of change of thickness at any point along the circumference is usually not in excess of 0.6 percent per degree of circumference, the leading and trailing faces of the blade being smooth and free of abrupt changes in thickness or curvature.

It will be apparent from FIGURES 4 and 6 to 9 that the leading spiral face 17 of each of the blades 9 and 10 intersects any plane containing the axis of rotation along t a concavely curved line generally perpendicular to the axis. The radius of curvature at any point on such curved line outwardly of the medial radius M is at least 0.4 times the radius of the blade and may be 10 or more times the radius of the blade in the vicinity of the leading portion 20. During the last quarter revolution of the blade (i.e., from the point i to the point r) the radius of curvature at any point outwardly of the medial radius M in any radial plane is preferably 0.5 to 2 times the radius of the blade and the center of curvature in said radial plane is preferably spaced from the axis of rotation a distance equal to about 0.5 to 0.9 times the radius of the blade so that the cross section of the blade is generally perpendicular to the axis. The radii of curvature at sections 44, 88, 9-0, 7-7, and 6-6 are identified as R to R respectively, in the drawings and are listed in Table II for purposes of illustration. This table has general application since the thickness and curvatures are indicated in relation to the radius R of the blade, but it will be understood that the numbers set forth in said table are approximate and may be varied considerably without losing all of the advantages of this It will be understood that the radius of curvature R at any point along the leading face 17 may be different from that at any other point. In Table II, R to R indicate the average radius of curvature in the particular radial section between the medial radius and the outer edge of the blade (i.e., between point 31 and point mn of FIGURE 6). The average radial curvature R at any radial section is preferably 0.5 to 3 times the radius of the blade considering the portion of the blade outwardly of the medial radius M During the first 90 of rotation (i.e., from the point a to point 11) such average radius curvature is usually greater than twice the radius of the blade. The average radius of curvature gradually decreases from the leading to the trailing edge. The reduction in the radius of curvature is usually less than one percent per degree of circumference. During the last quarter revolution (i.e., from the point It to the point s) the average radius of curvature (outwardly-of the medial radius) preferably decreases about 0.5 to 1 percent perdegree of circumference, the average radius of curvature in the last third of the blade (i.e., from point I to point 1') preferably being 0.5 to 1.5 times the radius R of the blade.

The radius of curvature of the outer portion of each blade is increased in a circumferential direction to cause application of suction and to increase this suction as the water passes through the screw. This minimizes cavitation problems and improves the efficiency of the screw.

It will be apparent that the marginal portion 36 of each of the blades 9 and 10 has less curvature than the thickened base portion 37 of the blade. Each of the rounded surfaces 38 and 39 of the base portion 37 preferably has an average radius of curvature at any radial section which is about 0.2 to about 0.3 times the radius R of the blade as indicated, for example, in FIGURES 6 to 9 which are drawn substantially to scale. In FIG- URE 8, R indicates the radius of curvature of the rounded surface 38 at the radial section 88.

In order to obtain maximum eti'iciency and high strength, each of the blades 9 and 10 is constructed so as to gradually increase in thickness in a circumferential direction from the leading end to the trailing end of the stantial part of the screw is above the water line.

blade. The portion of each blade outwardly of the medial radius M preferably has an average thickness which is .02 to .05 times the radius of the blade. The average thickness of such portion of the blade at various radial sections is indicated by t to in FIGURES 4 and 6 to 9 and in Table II. It will be apparent from the drawings that the rate of change in tldckness in a radial direction or a circumferential direction is gradual. Thus, in any radial section the leading edge at 17 is smooth and free of reversals in curvature from the hub to the periphery of the blade and the rate of change in thickness outwardly of the medial radius is substantially uniform.

- FIGURES 6 to 9 show points 31 to 34 located on the leading face 17 at various radial sections, said points being located at the medial radius M like the point 27 of FIGURE 2. The thickness of each of the blades at the medial radius gradually increases in a circumferential direction. Near the leading end portion 20 the thickness of the blade at the medial radius M is preferably about 0.2 to 0.3 times the radius of the blade, and near the trailing end portion 21 such thickness is preferably about 0.4 to 0.5 times the radius of the blade.

Outwardly of the medial radius M the thickness gradually decreases in a radial direction. In the first half of each blade (i.e., from point a to point i) the thickness of the blade in any radial section preferably decreases only .10 to 40 percent from the medial radius to a point near the marginal edge 25. In the last half of the blade (i.e.,

from point i to point r) the thickness in any radial plane preferably decreases 40 to 60 percent between the medial radius and a point near the periphery (i.e., between point 31 and marginal portion 36 in plane 6-6).

A line on surface 17 joining points 33 and c in FIG- URE 8 is almost perpendicular to the axis of rotation of the screw propeller, whereas a similar line from point 31 of FIGURE 6 is inclined somewhat. It will be understood that radial lines in the leading face 17 outward- .ly of M are inclined 80 to 90 degrees and usually 85 to 90 degrees relative to the axis of rotation generally as indicated in the drawings. A marine screw constructed substantially as shown in the drawings has excellent eiiiciency and will provide a boat or ship with a high speed.

Prior to this invention the pitch of marine propellers has been about 14 to 16 degrees. Higher pitches have been considered impractical because of serious cavitation problems and the inability of the propellers to carry the load. Those skilled in the art were unable .to provide eiiicient propellers with a pitch in excess of 18 degrees. The present invention permits manufacture of efficient marine screws with a pitch in excess of 22 degrees which are able to utilize efficiently the power of modern .engines (i.e., nuclear engines). The invention provides a practical method of overcoming cavitation problems and permits a substantial increase in the speed of a boat or ship without increasing the speed of rotation.

The screw of this invention has a further advantage in that it will transmit power effectively even when a. sub- It can propel the ship when only half of the screw is submerged. This simplifies the design of ships which carry heavy loads and eliminates serious problems when the ship is unloaded.

The screw propeller of this invention, when provided with a large diameter and a pitch of 20 degrees or more (i.e., 22 to 24) is ideal for use with extremely powerful engines such as nuclear power plants and provides the ship with extremely high speeds which could not be .ob-

tained with previously known propellers.

Unless the context shows otherwise, the radius of the blade is the distance from the axis of rotation to the outermost edge of the blade; a radial plane is a plane containing the axis of rotation; and the radius of curvetureis measured in a radial plane. It will be understood that the above description is by way of illustration rather than limitation and that, in accordance with the provisions of the patent laws, variations and modifications of the specific device shown herein may be made without departing from the spirit of the invention.

Having described my invention, I claim:

1. A marine screw for high speed ships comprising a hub and two coaxial blades of the same size and shape projecting radially from said hub and having corresponding portions spaced 180 degrees apart, each blade having an outermost helical edge of substantially constant radius describing an arc of about one-half revolution and having a relatively thin leading portion with a radially extending edge substantially perpendicular to the axis of rotation and a relatively thick trailing portion in the form of a rounded lobe which overlaps the leading portion of the other blade, each blade gradually increasing in thickness in a circumferential direction from said leading portion to said lobe and gradually decreasing in thickness from said hub to the radially outermost edge.

2. A marine screw as defined in claim 1 wherein said lobe has a smoothly curved trailing edge substantially in the form of an arc tangent to the radially outer edge of the blade, the radially outer half of said last-named are having a radius of curvature which is about 0.4 to 0.5 times the radius of said blade, and wherein said leading portion has a rounded outer edge extending radially a distance less than one-fifth the radius of the blade and a substantially straight cutting edge extending radially 0.4 to 0.5 times the radius of the blade.

3. A marine screw as defined in claim 2 wherein the thickness of the lobe of each blade is 30 to 60 percent greater. than the thickness of said leading portion of said blade, the average thickness of the blade changing no more than about 0.6 percent per degree of circumference.

.4. A marine screw comprising a hub and two integral coaxial blades of the same size and shape projecting radially from said hub and having corresponding portions spaced 180 degrees apart, each blade having a generally uniform pitch of 18 to 26 degrees and an outermost edge of substantially uniform radius extending circumferentially about one-half revolution, each blade having a lobe-shaped trailing portion at one end and a leading portion at the other end which overlaps the trailing portion of the other blade by at least 10 degrees, said leading portion having a cutting edge generally perpendicular to the axis of rotation, each blade having a spiral leading face which is radially concave to reduce cavitation and a spiral trailing face which is radially convex, the radial section of the blade at any radial plane throughout its circumference being inclined about 30 to degrees relative to the axis of rotation, each blade gradually decreasing in thickness in a radial direction from said hub to said outer most edge, the outer half of each blade having an average thickness at any radial plane which is about 0.02 to about 0.05 times the radius of the blade.

5. A marine screw as defined in claim 4 wherein each blade gradually increases in thickness from the leading portion to the trailing lobe portion, the average rate of change of thickness being about 0.2 to about 0.3 percent per degree of circumference, the maximum rate of change of thickness being not in excess of 0.6 percent per degree of circumference.

6. A marine screw as defined in claim 4 wherein the thickness of the blade at the medial radius measured in a plane through said leading portion and containing the axis of rotation is about 0.2 to about 0.3 times the radius of the blade and the thickness of the blade at the medial radius measured in a plane through said trailing portion and containing the axis of rotation is about 0.4 to 0.5 times the radius of the blade.

7. A marine screw as defined in claim 4 wherein the pitch is about 20 to 24 degrees and each blade. gradually increases in thickness from the leading end to the trailing end, the leading face of each blade having a concave '2 radial curvature which gradually increases from said leading end to said trailing end.

8. A marine screw for high speed ships comprising a hub and two integral pitched coaxial blades of the same size and shape projecting radially from said hub and having corresponding portions spaced 180 degrees apart, each blade having a generally uniform pitch and an outermost edge of substantially constant radius describing an arc of about one-half revolution, the trailing portion of one blade overlapping the leading portion of the other blade, the front leading face of each blade having concave radial curvature throughout its circumference and being free of reversals in radial curvature, the thickness of each blade gradually decreasing in a radial direction from said hub to the periphery and gradually increasing in a circumferential direction from the leading edge at one end of the blade to the trailing edge at the opposite end of the blade, the major portion of said leading edge outwardly of the medial radius being generally perpendicular to the axis, all of said trailing edge outwardly of the medial radius being in the form of a smooth curve with a radius of curvature greater than one-third the radius of each said blade, the radius of each said blade being about to 50 times the average thickness of the portion of the blade outwardly of the medial radius measured at any radial plane containing the axis of rotation.

9. A cast metal marine screw for high speed ships comprising a hub and two integral coaxial blades of the same size and shape projecting radially from said hub and having corresponding portions spaced 180 degrees apart, each blade having a generally uniform pitch of at least 18 degrees and an outermost edge describing an arc of about one-half revolution, the trailing end portion of one blade overlapping the leading end portion of the other blade, the leading spiral face of each blade intersecting any radial plane containing the axis along a concave-1y curved line generally perpendicular to the axis and having a radius of curvature at least about half the radius of the blade, said radius of curvature being about one-half to about two times the radius of the blade in radial planes containing said axis and located within 90 degrees of said trailing end portion, said radius of curvature gradually increasing in a circumferential direction away from said trailing portion.

10. A \marine screw as defined in claim 9 wherein each blade has a thickness of about 0.02 to 0.07 times the radius of the blade measured at the medial radius in any radial plane and gradually increases in thickness in a radial inward direction, the base of each blade being thickened and rounded in axial cross section to strengthen the blade and to facilitate flow of fluid over the blade, the radius of curvature R at the base of the blade measured in a radial plane being about 0.2 to about 0.3 times the radius of the blade.

11. A screw propeller comprising a hub and two integral coaxial blades of the same size and shape projecting radially from said hub and having corresponding portions spaced 180 degrees apart, each blade having a generally uniform pitch of at least 18 degrees and an outermost spiral edge of substantially constant radius extending circumferentially about one-half revolution, the thickness of each blade gradually decreasing in a radial direction from said hub to the periphery and gradually increasing in a circumferential direction from the leading end portion to the trailing end portion, the radius of each blade being about to about times the average thickness of the portion of the blade outwardly of the medial radius, any radial plane containing the axis of rotation of the propeller and within about one-quarter revolution of said leading end portion of the blade intersecting the leading face of the blade outwardly of the medial radius along a concavely curved line having a radius of curvature about 0.4 to about 2 times the radius of the blade, the center of curvature of any point on said curved line outwardly of said medial radius being spaced from the axis of rotation a distance equal to about 0.5 to about 0.9 times the radius of the blade, whereby the blade is generally perpendicular to said axis.

12. A marine screw for high speed ships comprising a hub and two coaxial blades of the same size and shape projecting radially from said hub and having corresponding portions spaced degrees apart, each blade having an outermost helical edge of substantially constant radius describing an arc of about one-half revolution and having a relatively thin leading portion with a radially extending edge substantially perpendicular to the axis of rotation and a relatively thick trailing portion in the form of a rounded lobe which overlaps the leading portion of the other blade, each blade gradually increasing in thickness in a circumferential direction from said leading portion to said lobe and gradually decreasing in thickness from said hub to the radially outermost edge, each blade having a thickened base portion with an average thickness at least three times the average thickness of the outer half of the blade, said base portion having smoothly curved side surfaces which intersect any radial plane along a curved line having a radius of curvature between about 0.2 and about 0.3 times the radius of the blade, the average thickness of the blade outwardly of the medial radius M being about 0.3 to 0.5 times the radius of the blade.

13. A screw as defined in claim 12 wherein the pitch of each blade is generally uniform throughout the circumference, the pitch at any point near the margin of the blade being about 16 to 20 degrees.

14. A marine screw as defined in claim 1 wherein the thickness of the lobe of each blade is 30 to 60 percent greater than the thickness of said leading portion of said blade, the average thickness of the blade changing no more than about 0.6 percent per degree of circumference.

15. A cast metal propeller comprising a hub and two integral coaxial blades of the same size and shape projecting radially from said hub and shaving corresponding portions spaced 180 degrees apart, each blade having a generally uniform pitch of about 18 to 20 degrees and extending circumferentially about half'of the circumference, each blade having a leading portion overlapping the trailing portion of the other blade, the major portion of the edge of each blade having a substantially constant radius and substantially constant angular pitch at the outermost surface of the blade, the thickness of each blade gradually decreasing in a radial direction from said hub to the periphery and gradually increasing in a circumferential direction from the leading end portion to the trailing end portion, the radius of each blade being about 20 to about 40 times the average thickness of the portion of the blade outwardly of the medial radius, any radial plane containing the axis of rotation of the proppeller and within about one-quarter revolution ofsaid leading end portion of the blade intersecting the leading face of the blade outwardly of the medial radius along a concavely curved line having a radius of curvature of about 0.4 to about 2 times the radius of the blade, the center of curvature of any point on said curved line outwardly of said medial radius being spaced from the axis of rotation at distance equal to about 0.5 to about 0.9 times the radius of the blade.

16. A marine propeller comprising a hub and two coaxial blades of the same size and shape projecting radially from said hub and having corresponding portions spaced 180 degrees apart, each blade having an outermost helical edge of substantially constant radius and substantially constant pitch extending about one-third to one-half the circumference of the propeller and having a relatively thin leading portion and a relatively thick trailing portion in the form of a rounded lobe which overlaps the leadingportion of the other blade, each blade gradually increasing in thickness in a circumferential direction from the leading portion to the trailing lobe portion, the average rate of change of thickness being about 0.2 to about 0.3 percent per degree of circumference, each blade having a thickness of about 0.2 to 0.07 times the radius of the blade measured at the medial radius in any radial plane and gradually increasing in thickness in a radial inward direction, the base portion of each blade being thickened and rounded in axial cross section, said base portion having an average thickness at least 3 times the average thickness of the outer half of the blade and having smoothly curved side surfaces which intersect any radial plane along a curved line, the leading face of each blade intersecting any radial plane containing the axis of rotation of the pnopeller and within about one-quarter revolution of the trailing end portion of that blade along a eonoavely curved line outwardly of the medial radius having a radius of curvature about 0.4 to about 2 times the radius of the blade, the center of curvature of any point on said curved line outwardly of said medial radius being spaced from the axis of rotation a distance equal to about 0.5 to about 0.9 times the radius of the blade.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Aircraft Propeller Design, by Fred E. Weick, published by McGraw-Hill Book Co., Inc.., New York and London, 1930.

EDGAR W. GEOGHEGAN, Primary Examiner.

EMILE PAUL, ABRAM BLUM, JULIUS E. WEST,

. Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,179 ,182 April 20 1965 Gyula Fuchs It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 9, line 2, for "0.2" read 0.02

Signed and sealed this 21st day of September 1965.

( SEAL) Attest:

ERNEST W. SWIDER I EDWARD J. BRENNER Atmsting Officer Commissioner of Patents 

1. A MARINE SCREW FOR HIGH SPEED SHIPS COMPRISING A HUB AND TWO COAXIAL BLADES OF THE SAME SIZE AND SHAPE PROJECTING RADIALLY FROM SAID HUB AND HAVING CORRESPONDING PORTIONS SPACED 180 DEGREES APART, EACH BLADE HAVING AN OUTERMOST HELICAL EDGE OF SUBSTANTIALLY CONSTANT RADIUS DESCRIBING AN ARC OF ABOUT ONE-HALF REVOLUTION AND HAVING A RELATIVELY THIN LEADING PORTION WITH A RADIALLY EXTENDING EDGE SUBSTANTIALLY PERPENDICULAR TO THE AXIS OF ROTATION AND A RELATIVELY THICK TRAILING PORTION IN THE FORM OF A ROUNDED LOBE WHICH OVERLAPS THE LEADING PORTION OF THE OTHER BLADE, EACH BLADE GRADUALLY INCREASING IN THICKNESS IN A CIRCUMFERENTIAL DIRECTION FROM SAID LEADING PORTION TO SAID LOBE AND GRADUALLY DECREASING IN THICKNESS FROM SAID HUB TO THE RADIALLY OUTERMOST EDGE. 